Initial Access Channel for Scalable Wireless Mobile Communication Networks

ABSTRACT

Physical layer structures and access schemes for use in such networks are described and in particular initial access channel (IACH) structures are proposed. A spectrum efficient downlink (DL) IACH design supports different types of User Equipment (UE) capabilities and different system bandwidths. An IACH includes the synchronization channel (SCH) and broadcast-control channel (BCH). A non-uniform SCH for all system bandwidths is provided, as well as scalable bandwidth BCH depending on system bandwidth. An initial access procedure is provided, as well as an access procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/759,388 filed Jan. 17, 2006, U.S. Provisional PatentApplication No. 60/722,744 filed Sep. 30, 2005, and U.S. ProvisionalPatent Application No. 60/814,417 filed Jun. 16, 2006, which are eachhereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to wireless mobile communication systems, and inparticular to physical layer structures and access schemes for use insuch networks.

BACKGROUND

In OFDM (Orthogonal Frequency Division Multiplexing) and OFDMA(Orthogonal Frequency Division Multiple Access) wireless communicationnetworks, data streams are typically transmitted in parallel usingmultiple orthogonal sub-carriers or tones within a single channel. Theuse of orthogonal sub-carriers allows the sub-carriers, spectra tooverlap, thus achieving high spectrum efficiency. An OFDM system mapscoded or modulated information symbols, QPSK (Quadrature Phase ShiftKeying) or QAM (Quadrature Amplitude Modulation) symbols for instance,to sub-carriers in the frequency domain, and then generates a timedomain signal for transmission using such a transformation technique asIFFT (Inverse Fast Fourier Transform). At a receiver, atime-to-frequency transformation, such as an FFT (Fast FourierTransform), is used to convert a received time domain signal into thefrequency domain. In order to recover transmitted source symbolscorrectly, the receiver aligns an FFT window with a corresponding IFFTwindow used at the transmitter and compensates for any frequency offsetbetween the transmitter and the receiver.

Initial access to a communication network by a communication terminalinvolves a search operation to find available base stations andcommunication channels and a synchronization operation to synchronizethe terminal to a base station. Dedicated physical channels, such as adownlink initial access channel (IACH) and a synchronization channel(SCH) for timing and frequency synchronization are used. A downlink IACHenables initial system access.

In wireless communication systems, the Base Transceiver Station (BTS)and User Equipment (UE) may have different transmission bandwidthcapabilities. For example, a BTS and a UE may each have scalablebandwidths from 1.25 MHz to 20 MHz. However, in prior art systems, thebandwidth of the IACH is equal to the system transmission bandwidth andis thus variable depending on the system transmission bandwidth. Thisassumes that the UE reception capability is always equal to or largerthan the transmission bandwidth. In prior art systems, a UE finds thesystem transmission bandwidth by changing the receive bandwidth and FFTsize. This approach requires longer access time and complexity.

SUMMARY OF THE INVENTION

A downlink initial access channel is described to support differenttypes of UE capabilities and different system bandwidths.

According to one aspect of the present invention, there is provided amethod of transmitting an access channel in a network having a systembandwidth, the access channel comprising a first channel and a secondchannel, the method comprising transmitting the access channel using abandwidth less than the system bandwidth.

According to another aspect of the present invention, there is provideda method of transmitting a communication signal, the communicationsignal comprising one or more frames being of the type that areregularly repeated, each frame comprising a plurality of time slots,each time slot comprising one or more OFDM symbols, the methodcomprising: inserting common pilot symbols in predetermined OFDMsymbols; inserting a SCH over some or all of the predetermined OFDMsymbols; transmitting the communication signal.

According to still another aspect of the present invention, there isprovided a method for decoding a BCH from a diversity transmitted signalcomprising: receiving a plurality of time domain OFDM signals from aplurality of transmit antennas to provide a received signal; decodingfrom the received signal a basic BCH without any information regardingthe number of transmit antennas; and decoding from the received signalan Extended BCH.

According to yet another aspect of the present invention, there isprovided a method of a UE performing initial access to a BTS comprising:performing initial timing and frequency synchronization based on a basicSCH; performing initial cell search based on the basic SCH; detectingthe basic BCH; obtaining system parameters; decoding a basic BCH and anExtended BCH; entering a connected mode; and performing sync trackingand cell search based on both the basic SCH and the Extended SCH.

According to a further aspect of the present invention, there isprovided a base transceiver station in a communication network, thecommunication network having a system bandwidth, the base transceiverstation comprising: a processor configured to select a bandwidth for anaccess channel less than the system bandwidth, and transmit the accesschannel.

Other aspects and features of the present invention will becomeapparent, to those ordinarily skilled in the art, upon review of thefollowing description of the specific embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference tothe accompanying diagrams, in which:

FIG. 1 is a block diagram of a wireless communication network;

FIG. 2 is a diagram of a known physical layer structure for a wirelesscommunication network;

FIG. 3A is a diagram illustrating spectrum allocation for a Primarycommon Synchronization Channel (PSC) for 5 MHz, 10 MHz and 20 MHztransmission bandwidths;

FIG. 3B is a diagram illustrating spectrum allocation for a PSC for 1.25MHz, and 2.5 MHz transmission bandwidths;

FIG. 4 is a diagram illustrating various examples of SCH spectrumallocations for 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz and 20 MHz transmissionbandwidths,

FIG. 5A is a diagram illustrating various examples of SCH and ExtendedSCH spectrum allocations for 1.25 MHz, 2.5 MHz, 5 MHz, and 10 MHztransmission bandwidths,

FIG. 5B is a diagram illustrating other examples of SCH and Extended SCHspectrum allocations for 1.25 MHz, 2.5 MHz, 5 MHz, and 10 MHztransmission bandwidths,

FIG. 5C is a diagram illustrating yet other examples of SCH and ExtendedSCH spectrum allocations for 1.25 MHz, 2.5 MHz, 5 MHz, and 10 MHztransmission bandwidths,

FIG. 6A is a diagram illustrating a first example for spectrumallocation for a SCH for 20 MHz transmission bandwidth;

FIG. 6B is a diagram illustrating a second example for spectrumallocation for a SCH for 20 MHz transmission bandwidth;

FIG. 7 is a diagram of the frequency domain structure of thebroadcast-control channel (BCH) for system bandwidths of 5 MHz, 10 MHzand 20 MHz;

FIG. 8 is a diagram of the frequency domain structure of the BCH forsystem bandwidths of 1.25 MHz and 2.5 MHz;

FIG. 9A is a diagram illustrating various examples of BCH and ExtendedBCH spectrum allocations for 1.25 MHz, 2.5 MHz, 5 MHz, and 10 MHztransmission bandwidths,

FIG. 9B is a diagram illustrating other examples of BCH and Extended BCHspectrum allocations for 1.25 MHz, 2.5 MHz, 5 MHz, and 10 MHztransmission bandwidths,

FIG. 10 is a diagram illustrating a spectrum allocation for a BCH for 20MHz transmission bandwidth;

FIG. 11A is a diagram of an example frame used in accordance with oneembodiment of the invention;

FIG. 11B is a diagram of a time domain structure of a PSC;

FIG. 11C is a diagram of Secondary Cell specific Sync Channel (SSC) andPSC locations for a Time Division Multiplex (TDM) based pilot design;

FIG. 11D is a diagram of SSC and PSC locations for a scattered pilotdesign;

FIG. 11E is a diagram of a one antenna and a four antenna irregulardiamond lattice scattered pilot pattern for OFDM symbols carrying a PSC;

FIG. 12A is a diagram of an example frame used in accordance with oneembodiment of the invention;

FIG. 12B is a diagram of the time domain structure for two PSC locationsused in accordance with one embodiment of the invention;

FIG. 13 is a diagram of time domain SCH multiplexing;

FIG. 14 is a flow chart of the possible steps that could be carried outin connection with an initial access procedure between a UE and a BTS;and

FIG. 15 is a flow chart of the steps carried out by a UE to access theSCH and BCH in one embodiment,

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a block diagram of a wireless communication network. Thecommunication network includes BTSs 10, 12, 14, which providecommunication network coverage to respective coverage areas or “cells”20, 22, 24. UE 16 is adapted to communicate with any of the BTSs 10, 12,14 within whose coverage areas the UE 16 is located.

The communication network shown in FIG. 1 is intended solely forillustrative purposes, and that a communication network may includefurther or different components than those explicitly shown in FIG. 1.For example, most communication networks include more than three BTSsand provide communication services for many UEs. Such communicationnetworks are also normally connected to other types of networks,including landline telephone networks, for instance. It should befurther appreciated that BTS coverage areas and UE ranges are notnormally purely hexagonal, and will include other areas of overlap.

Each BTS 10, 12, 14 includes a transceiver, or alternatively a separatetransmitter and receiver, for sending communication signals to andreceiving communication signals from the UE 16 via an antenna system. Anantenna system at a BTS may include a single antenna or a multipleantennas, such as in an antenna array, for example. The BTSs 10, 12, 14may also communicate with each other, and with other communicationstations or components, including components in other communicationnetworks, through wireless or wired communication links. Communicationfunctions of the BTSs may involve such operations as modulation anddemodulation, coding and decoding, filtering, amplification, andfrequency conversion. These and possibly other signal processingoperations are preferably performed in the BTSs by digital signalprocessors (DSPs) or general-purpose processors that execute signalprocessing software.

UE 16 is a wireless communication device such as a data communicationdevice, a voice communication device, a multiple-mode communicationdevice that supports data, voice, and possibly further communicationfunctions, or a wireless modem that operates in accordance with acomputer system. UE 16 receives communication signals from and/or sendscommunication signals to the BTSs 10, 12, 14 through a transceiver or areceiver and a transmitter, and an antenna system that may include asingle antenna or multiple antennas. As in the BTSs 10, 12, 14, suchsignal processing operations as modulation and demodulation, coding anddecoding, filtering, amplification, and frequency conversion may beperformed by a DSP or general-purpose processor in UE 16.

Communication signals between BTSs and UEs in a communication networkare formatted according to a particular protocol or communication schemefor which the communication network is adapted. Such signal formats arealso commonly referred to as physical layer structures.

An IACH is an initial acquisition channel for a mobile terminal such asUE 16 of FIG. 1 to access a communication network. For example, when UE16 is turned on, the device first receives the IACH transmitted from aBTS such as BTS 10. The IACH is used for one or more functions includinginitial access, synchronization, base station identification, andchannel estimation. More particularly, an IACH comprises controlinformation and includes an SCH and a BCH. An IACH can also be used forthe synchronization tracking and cell search for UEs in the connectedmode and idle mode.

FIG. 2 illustrates prior art system bandwidths structure 200 for awireless communication network in the frequency domain in an OFDMAnetwork where system bandwidths are scalable from 1.25 MHz, 2.5 MHz, 5MHz, 10 MHz and 20 MHz generally indicated at 200. Also illustrated at202 is the bandwidth of the IACH which is equal to the system bandwidthfor each of the 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz and 20 MHz scenarios.

Spectral efficiencies can be gained where the IACH is designed to have abandwidth less than the system bandwidth for at least some systembandwidths. Fast initial access can be supported by reduce the blindbandwidth search time with reasonable overhead.

The Spectrum Arrangement of a Synchronization Channel (SCH) and anExtended Synchronization Channel (Extended SCH)

An SCH is a logical channel used by mobile stations to achievetime/frequency synchronization with the network. An SCH enables (i) fastinitial system access; (ii) timing and frequency synchronization andtracking, (iii) fast cell selection and re-selection; (iv) lowcomplexity; (v) Downlink (DL) Continuous Quality Indicator (CQI)measurement; and (vi) channel estimation.

An SCH is typically comprised of two channels, a Primary SynchronizationChannel (PSC) and a Secondary Synchronization Channel (SSC). Thesynchronization process occurs when a UE is initially turned on and alsothereafter when the UE moves from one cell to another. Synchronizationis required because the UE does not previously have a set timing withrespect to the BTS. The PSC is detected in a first acquisition stage,which provides the UE of the timing of the communications. The SSC isdetected at a later acquisition stage, which provides the UE with moreaccurate timing information and a cell id.

The PSC may be modulated with the Primary Sync Sequences (PSS). The samePseudo-noise (PN) sequences across the whole network enable fast systemaccess and cell search.

An Extended SCH is used to improve ongoing cell search performance.

A first implementation of the invention is shown in FIGS. 3A and 3Bwhich illustrate two types of SCH (i)

Type 1 in FIG. 3A, for system bandwidths equal to or above 5 MHz, and(ii) Type 2 in FIG. 3B, for system bandwidths below 5 MHz. Asillustrated, the SCH bandwidth (as represented by PSC 508) is less thanthe system bandwidth where system bandwidth equals 20 MHz, 10 MHz and2.5 MHz). In the cases of 5 MHz and 1.25 MHz, the SCH bandwidth equalsthe system bandwidth. This allows for fast blind initial access by a UE.

BTS bandwidth information can be conveyed by the PSC for Type 1 and Type2. For Type 1: Three common PN sequences corresponding to three possiblesystem bandwidths: 5 MHz, 10 MHz and 20 MHz and (ii) Type 2: Two commonPN sequences corresponding to two possible system bandwidths: 1.25 MHzand 2.5 MHz. The time domain repetition structure of PSC symbol(s)allows the fast coarse synchronization. In Type 1, only half of thesub-carriers are modulated (see bottom portion of FIG. 3A). In Type 2,there may be two identical PSC symbols (see bottom portion of FIG. 3B).

As shown in FIG. 3A, for Type 1, the PSC 508 is located in 5 MHz in thecenter of the available band. In the case of 20 MHz system bandwidth502, PSC 508 takes up only 5 MHz of bandwidth, leaving 15 MHz ofleftover bandwidth 525. In the case of 10 MHz system bandwidth 504, PSC508 takes up only 5 MHz of bandwidth, leaving 5 MHz of leftoverbandwidth 525. In the case of 5 MHz system bandwidth 502, PSC 508 takesup all 5 MHz of bandwidth, leaving no leftover bandwidth. As illustratedin this Type 1 system, PSC 510 is modulated on half of the sub-carriers,leaving the other half of the sub-carriers to be null 512. The spectrumallocation displayed in FIG. 3A for various system bandwidths is merelyillustrative of one example of this embodiment.

As shown in FIG. 3B, for Type 2, the primary common SCH is located in1.25 MHz in the center of the available band. In the case of 2.5 MHzsystem bandwidth 530, PSC 508 takes up only 1.25 MHz of bandwidth,leaving 1.25 MHz of leftover bandwidth 525. In the case of 1.25 MHzsystem bandwidth 532, PSC 508 takes up all 1.25 MHz of bandwidth,leaving no leftover bandwidth. As illustrated in this Type 2 system, PSC510 is modulated on all of the useful sub-carriers. The spectrumallocation displayed in FIG. 3B for various system bandwidths is merelyillustrative of one example of this embodiment.

A further embodiment of the invention is now described. The basicsampling frequency (fs) and FFT size (Nfft) can be defined according tothe basic SCH bandwidth, which is chosen based on a trade-off of IACHdetection performance and UE minimum implementation complexity as wellas UE reception capability. The actual occupied bandwidth of the basicSC is determined by the basic SCH bandwidth, for example, around 4.5 MHzfor 5 MHz of basic SCH bandwidth.

Improved performance may be obtained from multiple basic SCHs when thesystem bandwidth and UE capacity is multiple times of the basic SCHbandwidth. Note that guard bands are used between basic IACHs to allowIACH acceptance by a UE with narrower than system bandwidth capacity.

Common sequence or sequences are transmitted by the PSC. All cells (orsectors) transmit the same sequence or the selected sequence from thesame sequence set.

FIG. 4 is a diagram illustrating various examples of frequency domainIACH structures. In the case of 20 MHz system bandwidth 610, SCH 602 isshown taking up intervals of approximately 4.5 MHz of bandwidth betweenguard bands 615. As noted above, improved performance may be obtainedfrom multiple basic SCHs when the system bandwidth and UE capacity ismultiple times of the basic SCH bandwidth.

In the 10 MHz bandwidth case 612, SCH 602 takes up approximately 4.5 MHzleaving approximately 5.5 MHz of leftover system bandwidth 604. In thecase of 5 MHz system bandwidth 614, SCH 602 takes up approximately 4.5MHz leaving approximately 1 MHz of leftover system bandwidth 604. In thecase of 2.5 MHz system bandwidth 616, SCH 602 takes up approximately 2MHz leaving approximately 0.5 MHz of leftover system bandwidth 604. Inthe case of 1.25 MHz bandwidth 618, SCH 602 takes up approximately 1 MHzleaving approximately 0.25 MHz of leftover system bandwidth 604. Thespectrum allocation displayed in FIG. 4 for various system bandwidths ismerely illustrative of one example of this embodiment. The values of4.5, 2 MHz and 1 MHz are only examples, the exact values are determinedby the specific implementation.

FIG. 5A is a diagram illustrating the spectrum allocation of a basic SCH1000 and an Extended SCH 1002. During initial access, a UE has noinformation about the transmission bandwidth. To simplify the initialcell search, a basic SCH 1000 of fixed narrow bandwidth, for example1.25 MHz, is used regardless of the overall transmission bandwidth. Thisbasic SCH 1000 of fixed narrow bandwidth (in this case, 1.25 MHz) isshown in connection with the case of 1.25 MHz system bandwidth 1010, 2.5MHz system bandwidth 1012, 5 MHz system bandwidth 1014, and 10 MHzsystem bandwidth 1016.

To support mobility, a UE still needs to perform the cell search afterinitial access. At this stage, the UE already knows the transmissionbandwidth of the serving BTS and even the neighbouring BTS through thebroadcast-control channel.

All useful sub-carriers in an SCH symbol are shared by the SCH and otherdata transmission. The basic SCH occupies the central 75 sub-carrierswhich in this example represents 1.25 MHz of bandwidth. For >1.25 MHztransmission bandwidth scenarios, the leftover spectrum could beoccupied by an Extended SCH and other data transmissions, depending onthe overall SCH bandwidth and the overall transmission bandwidth. In thecase where the Extended SCH does not occupy all of the leftoverspectrum, other traffic, for example broadcast-control information, canalso be transmitted by the same SCH symbol.

Accordingly, an Extended SCH 1002 can be defined to enhance the cellsearch performance in the connected mode and idle mode. The whole SCHwill therefore consist of two parts: (i) basic SCH 1000 used for initialaccess and occupied 1.25 MHz bandwidth, and (ii) Extended SCH 1002 whichis used to enhance the cell search performance.

The same SCH sequence with certain repetition or different SCH sequencecan be used by Extended SCH 1002. The advantage of this approach is lowSCH overhead, especially when SCH is transmitted multiple times in eachframe.

In the case of 1.25 MHz system bandwidth 1010, Extended SCH 1002occupies 0 MHz of bandwidth as basic SCH 1000 has occupied the entiretyof the spectrum. In the case of 2.5 MHz system bandwidth 1012, ExtendedSCH 1002 occupies 1.25 MHz of system bandwidth. In the case of 5 MHzsystem bandwidth 1014, Extended SCH 1002 occupies 3.75 MHz of bandwidth.In the case of 10 MHz system bandwidth 1016, Extended SCH 1002 occupies3.75 MHz of bandwidth. Other data traffic 1004 occupies 5 MHz ofbandwidth. The spectrum allocation displayed in FIG. 5A for varioussystem bandwidths is merely illustrative of one example of thisembodiment.

In another embodiment, basic SCH 1000 is transmitted through the central75 sub-carriers in each band, and the Extended SCH 1002 is transmittedby all leftover spectrums. The advantage of this solution is that thelow PAPR of a SCH symbol can be achieved when the cell common or cellspecific waveform is defined with as low a PAPR as possible. The averagetransmission power of a SCH symbol can be higher than other OFDMsymbols. This improves the cell search performance in some scenario,especially in the unsynchronized networks and for large cell size. Thecell search performance is improved proportionally with the increase ofthe overall transmission bandwidth. More SCH overhead is introduced ineach SCH symbol, especially for above 5 MHz transmission bandwidthcases. To reduce SCH overhead, SCH may be transmitted less frequently ineach frame. The basic SCH sequence should be the central portion of theoverall SCH sequence which has a low PAPR. The length of the total SCHsequence is equal to the overall length of basic SCH 1000 and theExtended SCH 1002.

FIG. 5B is a diagram illustrating the spectrum allocation of basic SCH1000 and Extended SCH 1002 in this alternative embodiment. In the caseof 1.25 MHz system bandwidth 1010, Extended SCH 1002 occupies 0 MHz ofbandwidth as basic SCH 1000 has occupied the entirety of the spectrum.In the case of 2.5 MHz system bandwidth 1012, basic SCH 1000 occupies1.25 MHz of bandwidth with Extended SCH 1002 occupying the remainder, or1.25 MHz of system bandwidth. In the case of 5 MHz system bandwidth1014, basic SCH 1000 occupies 1.25 MHz of bandwidth, with Extended SCH1002 occupying the remainder, or 3.75 MHz of bandwidth. In the case of10 MHz system bandwidth 1016, basic SCH 1000 occupies 1.25 MHz ofbandwidth, with Extended SCH 1002 occupying the remainder, or 8.75 MHzof bandwidth. In this case, Extended SCH 1002 is transmitted by allleftover spectrums and therefore there is no leftover bandwidth forother data traffic as there was in connection with the embodiment shownin FIG. 5A. The spectrum allocation displayed in FIG. 5B for varioussystem bandwidths is merely illustrative of one example of thisembodiment of the invention.

In another embodiment, a maximum SCH bandwidth, which is the total SCHbandwidth including the basic SCH and the Extended SCH, for example 5MHz, is defined. In this embodiment, if the overall spectrum is broaderthan the maximum SCH bandwidth, the unoccupied spectrum will not beused.

FIG. 5C is a diagram illustrating the spectrum allocation of a basic SCH1000 and an Extended SCH 1002 in this alternative embodiment. In thecase of 1.25 MHz system bandwidth 1010, Extended SCH 1002 occupies 0 MHzof bandwidth as basic SCH 1000 has occupied the entirety of thespectrum. In the case of 2.5 MHz system bandwidth 1012, basic SCH 1000occupies 1.25 MHz of bandwidth with Extended SCH 1002 occupying theremainder, or 1.25 MHz of system bandwidth. In the case of 5 MHz systembandwidth 1014, basic SCH 1000 occupies 1.25 MHz of bandwidth, withExtended SCH 1002 occupying the remainder, or 3.75 MHz of bandwidth. Inthe case of 10 MHz system bandwidth 1016, basic SCH 1000 occupies 1.25MHz of bandwidth, with Extended SCH 1002 occupying 3.75 MHz ofbandwidth. In this case, leftover bandwidth 1020 is left unused. Thespectrum allocation displayed in FIG. 5C for various system bandwidthsis merely illustrative of one example of this embodiment of theinvention.

In another embodiment, three options for SCH bandwidth and location for20 MHz transmission bandwidth are described. It is currently assumed bypersons skilled in the art that the maximum downlink transmissionbandwidth is 20 MHz. However the maximum UE reception capability is 10MHz. It is expected that a UE with 10 MHz reception capability willoperate in either the lower part of upper part of the full 20 MHztransmission band. To avoid inter-frequency measurement during aneighbour-cell measurement, it is desired that cell search be performedby a UE without re-tuning the centre carrier frequency in connected modeand idle mode.

The first option for this embodiment is shown in FIG. 6A. In thisembodiment, two identical SCHs, SCH A 1000A and SCH B 1000B aretransmitted in the lower band and the upper band of a 20 MHz systembandwidth spectrum 1018 separately. For the sake of clarity, SCH A 1000Aand SCH B 1000B are both being represented by SCH 1000 in the sameshading. Other data traffic 1004 occupies the remainder of the spectrumin both the upper band and lower band. In the lower half of FIG. 6A, a10 MHz reception bandwidth 1025 for a UE is shown. The spectrumallocation displayed in FIG. 6A for various system bandwidths is merelyillustrative of one example of this embodiment of the invention.

A second option for this embodiment is shown in FIG. 6B. In thisembodiment, a basic SCH 1000 is transmitted at the center of the 20 MHzsystem bandwidth spectrum 1018. Two Extended SCHs, Extended SCH A 1002Aand Extended SCH B 1002B are transmitted in the lower band and upperband separately though in different positions than as was shown in FIG.6A. Other data traffic 1004 occupies the remainder of the spectrum inboth the upper band and lower band. In the lower half of FIG. 6B, a 10MHz reception bandwidth 1025 for a UE is shown. For the sake of clarity,Extended SCH A 1002A and Extended SCH B 1002B are both being representedby SCH 1000 in the same shading. The spectrum allocation displayed inFIG. 6B for various system bandwidths is merely illustrative of oneexample of this embodiment. For example, basic SCH 1000 and Extended SCH1002A, 1002B could be transmitted alternatively in time.

The Spectrum Arrangement of a Broadcast-Control Channel (BCH) and anExtended Broadcast-Control Channel (Extended Broadcast-Control Channel)

A BCH is a downlink channel including specific parameters needed by a UEin order that it can identify the network and gain access to it. Typicalinformation includes the Location Area Code (LAC), Routing Area Code(RAC), and the Mobile Network Code (MNC), and other system parameters.

A BCH can be located at any predetermined location in each frame. Theoverall BCH includes a basic BCH and an Extended BCH. A basic BCH isused to transmit the information to a UE with at least the samebandwidth capabilities as the minimum bandwidth supported by each type.The basic BCH transmits important system parameters, including antennaconfiguration, overall transmission bandwidth, the bandwidth of theExtended SCH, the bandwidth of the Extended BCH, and the cyclic prefixlength. An Extended BCH transmits other broadcast-control signalingincluding the information for the UE above the available systembandwidth capabilities.

The frequency domain arrangement of BCH is described as follows. Thebasic BCH originates at the left end of the spectrum. The Extended BCHoccupies the leftover available spectrum. Guard bands may be requiredbetween the basic BCH and Extended BCH as well as between the ExtendedBCHs.

FIG. 7 is a diagram of the frequency domain structure of the BCH in thisembodiment for system bandwidths from 5 MHz to 20 MHz. In the case of 5MHz system bandwidth 920, basic BCH 902 takes up all of the availablesystem bandwidth. In the case of 10 MHz system bandwidth 922, basic BCH902 takes up 5 MHz of bandwidth, and Extended BCH 904 takes up theremainder of the system bandwidth. Extended BCH 904 is designed to beused for a UE with receive capabilities over 5 MHz. In the case of a 20MHz system bandwidth 924, basic BCH 902 takes up 5 MHz of bandwidth, andExtended BCH 904 takes up an additional 5 MHz of system bandwidth.Extended BCH 906 is available to be used for the remainder of the systembandwidth. Extended BCH 906 is used for UE with receiving capabilitiesover 10 MHz. The spectrum allocation displayed in FIG. 7 for varioussystem bandwidths is merely illustrative of one example of thisembodiment.

FIG. 8 is a diagram of the frequency domain structure of the BCH in thisembodiment for system bandwidths of 1.25 MHz and 2.5 MHz bandwidth. Inthe case of 1.25 MHz system bandwidth 954, basic BCH 950 takes up all ofthe available 1.25 MHz of bandwidth. In the case of 2.5 MHz systembandwidth 956, basic BCH 950 takes up 1.25 MHz of bandwidth, andExtended BCH 952 takes up an additional 1.25 MHz of system bandwidth.The spectrum allocation displayed in FIG. 8 for various systembandwidths is merely illustrative of one example of this embodiment.

In FIG. 9A, one example of a spectrum arrangement for a BCH (i.e. basicBCH 1050 and an Extended BCH 1052) is shown. The bandwidth of theExtended BCH will vary depending on the overall system transmissionbandwidth. The BCH bandwidth will increase with greater transmissionbandwidth.

In the case of 1.25 MHz system bandwidth 1010, Extended BCH 1052occupies 0 MHz of bandwidth as basic BCH 1050 has occupied the entiretyof the spectrum. In the case of 2.5 MHz system bandwidth 1012, basic BCHoccupies 1.25 MHz of bandwidth with Extended BCH 1052 occupying theremainder, or 1.25 MHz of system bandwidth. In the case of 5 MHz systembandwidth 1014, basic SCH 1050 occupies 1.25 MHz of bandwidth, withExtended BCH 1052 occupying the remainder, or 3.75 MHz of bandwidth. Inthe case of 10 MHz system bandwidth 1016, basic BCH 1050 occupies 1.25MHz of bandwidth, with Extended BCH 1052 occupying the remainder, or8.75 MHZ of bandwidth. In this case, Extended BCH is transmitted by allleftover spectrums and therefore there is no leftover bandwidth forother traffic. The spectrum allocation displayed in FIG. 9A for varioussystem bandwidths is merely illustrative of one example of thisembodiment of the invention.

In another example of this embodiment, all useful sub-carriers in a BCHsymbol are shared by the broadcast-control channel and other datatransmission. Therefore, a maximum BCH bandwidth is defined, which isthe total BCH bandwidth (for example 5 MHz) including the basic BCH andthe Extended BCH. In this example of 5 MHz BCH bandwidth, each BCHoccupies the central 75 subcarriers. For >1.25 MHz transmissionbandwidth scenarios the leftover spectrum could be occupied by ExtendedBCH and other data transmission, depending on the overall BCH bandwidthand the overall transmission bandwidth.

FIG. 9B is a diagram illustrating the spectrum allocation of a basic BCH1050 and an Extended BCH 1052 in this alternate example. In the case of1.25 MHz system bandwidth 1010, Extended BCH 1052 occupies 0 MHz ofbandwidth as basic BCH 1050 has occupied the entirety of the spectrum.In the case of 2.5 MHz system bandwidth 1012, basic BCH 1050 occupies1.25 MHz of bandwidth with Extended SCH 1052 occupying the remainder, or1.25 MHz of system bandwidth. In the case of 5 MHz system bandwidth1014, basic BCH 1050 occupies 1.25 MHz of bandwidth, with Extended BCH1052 occupying the remainder, or 3.75 MHz of bandwidth. In the case of10 MHz system bandwidth 1016, basic BCH 1050 occupies 1.25 MHz ofbandwidth, with Extended BCH 1052 occupying 3.75 MHz of bandwidth. Inthis case, any leftover bandwidth is occupied by other data traffic1004. The spectrum allocation displayed in FIG. 9B for various systembandwidths is merely illustrative of one example of this embodiment ofthe invention.

In another example, BCH bandwidth and location for 20 MHz transmissionbandwidth is described. To allow a 10 MHz capability UE to detect a BCHwhen directed at either side of the overall 20 MHz transmission bandwithout a change of the carrier frequency, a BCH should be transmittedtwice: once in the lower 10 MHz band and once upper 10 MHz band. Boththe basic BCH and the Extended BCH are transmitted in the two 10 MHzbands. The same maximum BCH bandwidth can be used as in othertransmission bandwidth scenarios described above.

This example is shown in FIG. 10 which is a diagram illustrating aspectrum allocation for a BCH for 20 MHz transmission bandwidth. In thisembodiment, two identical BCHs, comprised of basic BCH A 1050A andExtended BCH A 1050A, and basic BCH B 1050B and Extended BCH B 1052B,are transmitted in the lower band and the upper band of a 20 MHz systembandwidth spectrum 1018 separately. For the sake of clarity, basic BCH A1050A and basic BCH B 1050B are both being represented by basic BCH 1050in the same shading. Likewise, Extended BCH A 1052A and Extended BCH B1052B are both being represented by basic BCH 1052 in the same shading.Other data traffic 1004 occupies the remainder of the spectrum in boththe upper band and lower band. In the lower half of the figure, a 10 MHzreception bandwidth 1025 for a UE is shown. The spectrum allocationdisplayed in FIG. 10 for various system bandwidths is merelyillustrative of one example of this embodiment of the invention. Forexample, basic BCH A 1050A and Extended BCH A 1050A, and basic BCH B1050B and Extended BCH B 1052B could be transmitted alternatively in thelower band the upper band.

Time Domain Structure for SCH and BCH

According to an embodiment of the invention common pilots may be used asa SCH or part of a SCH for OFDMA. According to one embodiment, thecommon pilots are used as a synchronization channel for DLcommunications as follows:

Reuse some or all common pilot sub-carriers to transmit SCH, i.e. thePSC and the SSC. This reduces overhead and pilot density may be changedaccording to the channel condition. For TDM based pilot format, commonpilot symbols may be modulated by primary common Sync sequence (PSS) andsecondary cell specific Sync sequence (SSS) alternatively. For scatteredpilot format, common pilot sub-carriers may be shared by PSC and SSC.

In a first option, scattered pilots in each TTI may assigned to the PSCand SSC. For example, the pilot sub-carriers in the first symbol (orsymbol pair) may be assigned to SSC and the pilot sub-carriers in the4th (and 5th) symbols may be assigned to PSC. In a second option, thepilot sub-carriers in the 4th (and 5th) symbols in the last TTI perframe are used for PSC. To enable the fast system access, only half ofthe sub-carriers may be modulated.

FIG. 11A is a diagram of an example frame 302 for transmission used inaccordance with one embodiment of the invention. More particularly, FIG.11A illustrates a first embodiment where there are two types of SCH, aPSC and an SSC, in a system bandwidth greater than or equal to 5 MHz.FIG. 11A is only one example of a frame structure that can be used inaccordance with this embodiment of the invention.

Shown is frame 302 which in this example of 10 ms duration. Not shown isframe N−1 which precedes frame 302 and Frame N+1 which follows frame302. Frame 302 is comprised of a plurality of Transmission TimeIntervals (TTI) TTI-1 304, TTI-2 306, TTI-3 308, TTI-4 310, TTI-19 312and TTI-20 314. For the sake of clarity, the TTIs between TTI-4 310 andTTI-19 312 are not shown. In this representative example, each TTI is of0.5 ms duration, though 0.5 ms TTI is only an example. Therefore, inthis example, there are a total of 20 TTIs in frame 302. Each TTIcomprises seven OFDM symbols

In this embodiment, SSC 316 is transmitted in an OFDM symbol located atthe beginning of each TTI in frame 302. BCH 322 is transmitted in anOFDM symbol located at the end of TTI-20 314. PSC 320 is transmitted inan OFDM symbol located immediately preceding BCH 322 in TTI-20 318.Optionally, SSC 318 can also be transmitted in an OFDM symbol located inthe middle of each TTI.

One benefit to locating cell specific synchronization channel such asSSC 316 at the beginning of each TTI is that UE's for which there is notraffic in the remaining six symbols need not process these lattersymbols. It is not necessary to locate synchronization information inthe first OFDM symbol to realize a benefit. Instead, benefits can beachieved by locating such information in a dedicated OFDM symbol. TheSSC can be used as pilots to assist channel estimation, channel qualitymeasurement and cell search. There is a power saving feature for a UEwhich only needs to do the cell search and the channel qualitymeasurement.

In FIG. 11B, the time domain structure of PSC 320 is shown. Asillustrated, PSC 320 is comprised of prefix 324, following by twoidentical parts 323 and 326. Prefix 324 may be a cyclic prefix. This isonly one embodiment and it is not absolutely necessary for PSC 320 tohave two identical parts.

FIG. 11C illustrates another example of SSC and PSC locations for a TDMbased pilot design. In this embodiment, SSC 316 is transmitted in thefirst OFDM symbol of each TTI in frame 302. PSC 320 is transmitted inthe first OFDM symbol of each TTI other than TTI-1 304 (i.e. TTI-2 306,TTI-3 308, . . . TTI-20 314).

FIG. 11D illustrates SSC and PSC locations for a scattered pilot design.In this embodiment, SSC 316 is transmitted in the first OFDM symbol ofTTI-1 304 and in the first OFDM symbol of TTI-20 314 of frame 302. PSC320 is transmitted in the fourth and fifth OFDM symbols of TTI-1 304 andTTI-20 314.

FIG. 11E is an example pilot pattern which can be used in accordancewith one embodiment of the present invention. Pilot and data symbols arespread over an OFDM sub-frame in a time direction 120 and a frequencydirection 122. Most symbols within the OFDM sub-frame are data symbols124. Pilot symbols 126 are inserted into some of the OFDM symbols ineach TTI. The PSC and SSC can be transmitted over these symbols.

FIG. 12A is a diagram of an example frame 402 used in accordance withone embodiment of the invention. More particularly, FIG. 12A illustratesa second embodiment, in a Type-2 system, i.e. a system bandwidth lessthan 5 MHz. FIG. 12A is only one example of a frame structure that canbe used in accordance with this embodiment of the invention.

Shown is frame 402 which in this example of 10 ms duration. Not shown isframe N−1 which precedes frame 402 and Frame N+1 which follows frame402. Frame 402 is comprised of TTI-1 404, TTI-2 406, TTI-3 408, TTI-4410, TTI-19 412 and TTI-20 414. For the sake of clarity, the TTIsbetween TTI-4 410 and TTTi-19 412 are not shown. In this representativeexample, each TTI is of 0.5 ms duration. Therefore, in this example,there are a total of 20 TTIs frame 402.

In this embodiment, SSC 416 is transmitted in a slot located at thebeginning of each TTI in frame 402. BCH 422 is transmitted in a slotlocated at the end of TTI-20 414. A first PSC 420 is transmitted in aslot located immediately preceding BCH 322 in TTI-20 318. A second PSC421 is transmitted immediately preceding PSC 420. Optionally, SSC 318can also be transmitted in a slot in the middle of each TTI.

In FIG. 12B, the time domain structure of PSC 420 and PSC 421 is shown.As illustrated, PSC 420 and PSC 421 are both comprised of prefix 424,following by part 425.

FIG. 13 is a diagram of time domain SCH multiplexing. As shown, SCH 575is illustrated to be transmitted periodically. As illustrated, SCH 575is transmitted in a slot at the beginning of each of Frame N 576 andFrame N+1 578. For the sake of clarity, the preceding and succeedingframes are not illustrated.

Initial Access Procedure

In general, the initial access procedure between a UE and a BTScomprises the following steps:

1. Primary SCH bandwidth identification: SCH bandwidth selection basedon UE's capability and/or system bandwidth.

Option-1:

UE determines the type of SCH according to its capability. UE thendetects the Primary SCH using the bandwidth determined by the SCH type.

Option-2:

UE detects the Primary SCH using fs and Nfft determined by the basic SCHbandwidth. Multiple basic SCH may be detected if both the systembandwidth and UE capability are above certain multiples of bandwidth ofthe basic SCH.

2. Frame acquisition. Coarse timing synchronization based on time domainrepeated primary SCH structure.

3. Timing acquisition

4. Frequency acquisition

5. System bandwidth identification

6. BCH detection

7. Cell identification and selection

8. Fine frequency synchronization

9. Fine timing verification

Note that the order of steps 5 and 6 above can be exchanged. For examplethe system bandwidth information can be obtained from BCH if BCH can bedecoded at first.

FIG. 14 is a flow chart of the possible steps that could be carried outin connection with an initial access procedure between an UE and a BTS.At step 960, a UE determines the type of SCH according to itscapability. The UE detects the Primary SCH using the bandwidth (orsampling frequencies and FFT size (Nfft)) determined by the SCH type.Alternatively, the UE detects the Primary SCH using frequencies and Nfftdetermined by the basic SCH bandwidth. Multiple basic SCH may bedetected if both the system bandwidth and UE capability are abovecertain times the bandwidth of the basic SCH.

At step 962, frame acquisition takes place. Coarse timingsynchronization is based on time domain repeated primary SCH structure.At step 964, system bandwidth detection and fine timing acquisitiontakes place. The system bandwidth information is carried by the Primarysynchronization sequences, for example there are several sequences whichcorresponding to different system BW. At step 966, coarse frequencysynchronization in the time domain takes place. At step 968, fine timingis the frequency domain is carried out based on selected PSS. At step970, the UE find the maximum of the cross correlation and performs cellcorrelation based on SSS.

At step 972, fine frequency synchronization is performed in thefrequency domain. At step 974, fine timing synchronization verificationis performed (i.e. a correlation between the recovered and the originalcell specific PN code corresponding to the selected cell). At step 976,an evaluation is performed as to whether the correlation value is abovea certain threshold. If not, the procedure is repeated at step 960. Ifso, there is BCH detection according to system bandwidth and UEcapability at step 980. At step 982, the fine sync and broadcast controlinformation is output.

In other embodiments, a spectrum arrangement of the SCH and BCH is setout. As noted above, a UE needs to detect the SCH and BCH during initialaccess. However, such connectivity is also required during the connectedmode (i.e. there is an always-on connection between the UE and the BTS)and the idle mode (i.e. the UE is still connected to the BTS, but notreceiving or demodulating any downlink signals during the packettransmission intermission interval, and thus power is saved).

During initial access, the UE first detects the central part of thespectrum (i.e. center carrier frequency) regardless of the transmissionbandwidth of the UE and that of the BTS. Transmission is then initiatedusing the assigned spectrum.

In accordance with this embodiment, a UE can detect the SCH and BCH inthe connected and idle mode without returning to the center carrierfrequency. Transmit diversity can be applied to the SCH and BCH toimprove the coverage when there are more than one transmit antennapresent in BTS, though the transmit diversity scheme should be in somecases transparent to the UE, at least for the initial access.

Transmit Diversity Scheme for BCH

In yet another embodiment, a transmit diversity scheme for a BCH isdescribed. Transmit diversity can be applied by a BTS with more than oneTx antenna to improve the coverage.

Candidate transmit diversity schemes include (i)

Block code based transmit diversity. With this transmit diversityscheme, knowledge of the number of transmit antennas is needed by theUE, (ii) Frequency switched transmit diversity (sub-carrier based FSTD).With this transmit diversity scheme, there is no need for the UE to knowthe number of transmit antennas if the channel estimation is done basedon SCH with the similar structure, and (iii) Cyclic delay diversity(CDD). Blind detection may be required for channel estimation if thereis no antenna configuration information, and (iv) Time switched transmitdiversity (symbol based TSTD). In this case, more than one BCH symbol isrequired to achieve the diversity.

Usually, the UE has no a priori knowledge of the number of transmitantennas when decoding a BCH. It is desired that the transmit diversityscheme be transparent to UE, at least for the initial BCH detection.

Two options for a Tx diversity scheme for BCH are preferred: (i) inOption 1: Either FSTD or CDD can be used to decode the basic BCH and theExtended BCH. (ii) In Option 2: Either of FSTD and CDD can be used todecode the basic BCH, and block code based transmit diversity is used todecode the Extended BCH. In Option 2, the UE will detect the number oftransmit antennas from the basic BCH. The UE will decode the ExtendedBCH accordingly.

Where the antenna configuration can be obtained before the decoding ofBCH, in this case a block code based transmit diversity scheme can beapplied to both the basic BCH and the Extended BCH. For FSTD, thesub-carriers used to transmit the data are mapped to different antennasalternatively on the sub-carrier base. For example, the odd indexedsub-carriers are mapped onto antenna-1 and the even indexed sub-carriersare mapped onto antenna-2. The mapping could be swapped between antennasin different transmission instances.

Access Procedure

In another implementation, an access procedure is described. A flowchart of the steps carried out by a UE to access the SCH and BCH are setforth in FIG. 15. At step 1610, a UE performs an initialtiming/frequency synchronization based on the basic SCH. At step 1620,the UE performs initial cell search based on the basic SCH. At step1630, the UE detects the basic BCH. At step 1640, the UE obtains basicsystem parameters. At step 1650, the UE decodes the Extended BCH. Atstep 1660, the UE enters the connected mode. Finally, at step 1670, theUE performs Sync tracking and cell search based on both the basic SCHand the Extended SCH.

What has been described is merely illustrative of the application of theprinciples of the invention. Other arrangements and methods can beimplemented by those skilled in the art without departing from thespirit and scope of the present invention.

1. A method of transmitting an access channel in a network having asystem bandwidth, the access channel comprising a first channel and asecond channel, the method comprising: transmitting the access channelusing a bandwidth less than the system bandwidth.
 2. The method of claim1 wherein the first channel is a Synchronization Channel (SCH).
 3. Themethod of claim 1 wherein the second channel is a Broadcast-controlChannel (BCH).
 4. (canceled)
 5. (canceled)
 6. The method of claim 1,wherein when the system bandwidth is 20 MHz, a plurality of firstchannels are repeated within the system bandwidth between guard bandsadjacent to each first channel.
 7. (canceled)
 8. (canceled)
 9. Themethod of claim 1, further comprising transmitting an ExtendedSynchronization Channel (Extended SCH) of variable bandwidth up to theremainder of the system bandwidth.
 10. (canceled)
 11. (canceled)
 12. Themethod of claim 1, further comprising transmitting an ExtendedBroadcast-control Channel (Extended BCH) of variable bandwidth up to theremainder of the system bandwidth.
 13. (canceled)
 14. (canceled)
 15. Amethod of transmitting a communication signal, the communication signalcomprising one or more frames being of the type that are regularlyrepeated, each frame comprising a plurality of time slots, each timeslot comprising one or more OFDM symbols, the method comprising:inserting common pilot symbols in predetermined OFDM symbols; insertinga SCH over some or all of the predetermined OFDM symbols; transmittingthe communication signal.
 16. The method of claim 15 wherein the SCHcomprised comprises a first Secondary cell specific SynchronizationChannel (SSC).
 17. The method of claim 15 wherein the SCH comprises aPrimary Synchronization Channel (PSC) inserted into the second-to-lasttime slot of the frame.
 18. The method of claim 15 wherein the SCHcomprises a Broadcast-control channel inserted into the last OFDM symbolof the last time slot of the frame.
 19. The method of claim 18 wherein asecond SSC is inserted into an OFDM symbol, other than the first OFDMsymbol, of each time slot of the frame.
 20. The method of claim 19wherein the second SSC is inserted into the fourth OFDM symbol of eachtime slot of the frame.
 21. (canceled)
 22. (canceled)
 23. (canceled) 24.A method for decoding a BCH from a diversity transmitted signalcomprising: receiving a plurality of time domain OFDM signals from aplurality of transmit antennas to provide a received signal; decodingfrom the received signal a basic BCH without any information regardingthe number of transmit antennas; and, decoding from the received signalan Extended BCH.
 25. The method of claim 24 wherein the basic BCH isdecoded using one of a frequency switched transmit diversity (FSTD)scheme and a cyclic delay diversity scheme (CDD) and the Extended BCH isdecoded using one of a FSTD and CDD scheme.
 26. The method of claim 25wherein the Basic BCH is decoded using one of a FSTD scheme and theExtended BCH is decoded using a block code based transmit diversityscheme.
 27. A method of a UE performing initial access to a BTScomprising: performing initial timing and frequency synchronizationbased on a basic SCH; performing initial cell search based on the basicSCH; detecting the basic BCH; obtaining system parameters; decoding abasic BCH and an Extended BCH; entering a connected mode; and performingsync tracking and cell search based on both the basic SCH and theExtended SCH.
 28. A base transceiver station in a communication network,the communication network having a system bandwidth, the basetransceiver station comprising: a processor configured to select abandwidth for an access channel less than the system bandwidth, andtransmit the access channel.
 29. The base transceiver station of claim28, wherein the processor is further configured to transmit an ExtendedSCH.
 30. The base transceiver station of claim 28, wherein the processoris further configured to transmit an Extended BCH.